Apparatus and method for input channel isolation within an electronic test instrument

Abstract

An electrical isolation device wherein a signal to be electrically isolated is mixed with a carrier signal by a multiplier to produce a modulated carrier signal which is passed through an isolation barrier and demodulated and filtered to extract thereby the initial input signal.

1. Apparatus, comprising:
 a modulator, for modulating an input signal onto a carrier signal to produce a modulated carrier signal, said modulator being coupled to a first ground reference; 
 a demodulator, for receiving a representation of said modulated carrier signal and a representation of said carrier signal for demodulating said representation of modulated carrier signal to produce a demodulated signal, said demodulator being coupled to a second ground reference, said first and second ground references being electrically isolated from each other; 
 an isolator for receiving said modulated carrier signal from said modulator, producing said representation of modulated carrier signal, and conveying said representation of modulated carrier signal to said demodulator while maintaining said isolation of said first and second ground references; and 
 a filter, for retrieving a corresponding input signal from said demodulated signal. 
 
   
   
     2. The apparatus of  claim 1 , wherein said modulator comprises a switch operating to multiply the input signal by ±1 in response to the carrier signal. 
   
   
     3. The apparatus of  claim 1 , wherein said modulator and demodulator comprise balanced mixers. 
   
   
     4. The apparatus of  claim 1 , wherein said isolator comprises a transformer. 
   
   
     5. The apparatus of  claim 4 , wherein said isolator comprises a pulse transformer and said carrier signal comprises a square wave having a frequency greater than twice the frequency of said input signal. 
   
   
     6. The apparatus of  claim 1 , further comprising:
 an oscillator for generating said carrier signal, said oscillator being coupled to one of said first and second ground references, said oscillator having an output directly coupled to one of said modulator and said demodulator; and 
 a second isolator receiving said carrier signal and conveying a representation of said carrier signal to the other of said modulator and said demodulator while maintaining said isolation of said first and second ground references. 
 
   
   
     7. The apparatus of  claim 6 , wherein:
 said first and second isolators comprise transformers. 
 
   
   
     8. The apparatus of  claim 7 , wherein:
 said carrier signal and said representation of said carrier signal comprise respective square wave signals having a common predetermined frequency. 
 
   
   
     9. The apparatus of  claim 8 , wherein said predetermined frequency is less than an input signal frequency. 
   
   
     10. The apparatus of  claim 1 , wherein said filter comprises at least one of a Bessel filter, a Gaussian filter and an Elliptical filter. 
   
   
     11. A test and measurement instrument, comprising:
 a modulator, for modulating an input signal onto a carrier signal to produce thereby a modulated carrier signal, said modulator being coupled to a first ground reference; 
 a demodulator, for receiving a representation of said modulated carrier signal and a representation of said carrier signal for demodulating said representation of modulated carrier signal to produce a demodulated signal, said demodulator being coupled to a second ground reference, said first and second ground references being electrically isolated from each other, 
 an isolator for receiving said modulated carrier signal from said modulator, producing said representation of modulated carrier signal, and conveying said representation of modulated carrier signal to said demodulator while maintaining said isolation of said first and second ground references; and 
 a filter, for retrieving a corresponding input signal from said demodulated signal.